The present invention relates to infra-red motion detectors of the type used in residential outside lighting, for example, to illuminate a walkway or driveway when a person or automobile approaches.
Lighting devices responsive to the infra-red radiation emitted by humans or motor vehicles have been known for some time. These devices turn on a light when they receive infra-red radiation from a person or vehicle moving in the field of view of the device. Such lighting devices are desirable because they improve safety by automatically providing a lighted path for approaching guests, they save energy by automatically turning off the lights when no one is nearby, and they improve security by illuminating the area when an unwanted intruder approaches. The devices are coupled to a motion detector unit which includes a sensor responsive to infra-red radiation and an arrangement of lenses or mirrors for directing infra-red radiation from an approaching person or object to the sensor. The motion detector with its lenses or mirrors must be positioned in full view of the area to be monitored so that the device can "see" approaching persons or other target objects.
The typical lighting fixture by the front door of a house is decoratively designed, often characteristic of a particular stylistic period complementing the style of the house. The motion detector unit in known decorative lighting fixtures is a self-contained unit mounted in the vicinity of the lighting fixture as an adjunct to the fixture. Typically an extra mounting base is supplied to hold the motion detector unit and associated circuitry, and the lighting fixture is separately mounted on the mounting base.
FIG. 1 illustrates the problems in mounting a decorative lighting fixture with motion detector unit according to known practice. A mounting base 10, illustrated in phantom, is mounted on an exterior sidewall of a house located, for example, by the front door. A motion detector unit 11 (also shown in phantom) and lighting fixture 12 are mounted on base 10. A first problem with this mounting method is that an extra mounting base 10 must be supplied with the lighting fixture, which adds to the inventory of parts that must be maintained and amount of the product packaging. Another problem evident from FIG. 1 is that not all lighting fixtures can be functionally mounted in this manner. The lighting fixture illustrated in FIG. 1, for example, is a popular design including a long, downwardly extending, decorative tail piece 13. In the conventional mounting method the tail piece necessarily obstructs the field of view, indicated at reference numeral 14, of motion detector unit 11. Thus, the conventional method may practically be used only with lighting fixtures of limited outline leaving a clear area for the motion detector field of view. To avoid this problem, mounting base 10 may of course be made larger to extend beyond the lighting fixture outline, but this results in an undesirable tradeoff. To the supplier or producer of the lighting fixtures, providing a larger mounting base sufficient to avoid the lamp outline calls for yet a greater parts inventory to match a variety of lamp outlines, calls for more product packaging, and ultimately increases the cost of the fixture. To the consumer the necessity of a larger mounting base highlights another problem with the conventional mounting method. A conventional mounting base and motion detector unit do not generally conform to the style of the lighting fixture. The base and motion detector unit can appear incongruent and out of place because they do not follow the lines of the fixture design or because they visibly impose an unwanted piece of twentieth-century electronics into an old-world lamp design.